This invention relates to method and apparatus for determining the position and orientation of a target with respect to a sensor. Both the target and the sensing unit may be affixed to movable objects, although generally the target will be stationary, and the sensing unit will be attached to a self-propelled vehicle. In a preferred embodiment of this invention, a target member is attached to a pallet, and the position and orientation information is used in the maneuvering of an automatically guided forklift truck to the pallet.
There are many prior art devices which attempt to determine the location of a vehicle with respect to a target. In these devices, the vehicle carries a sensing unit, the output of which controls some function of the vehicle, such as its forward motion, steering control or the vertical location of the forks. The target might be the pallet itself or the frame or rack on which the pallet is supported. Some of the prior art devices employ specialized marks whose dimensions are known; others utilize special light projectors and sense the light reflected from the target for positioning a vehicle, or a component of the vehicle, such as the forks of a lift truck.
When using a plurality of marks located on the target, it is difficult, and becomes close to impossible, to determine accurately all six degrees of freedom, that is, horizontal position--right and left, horizontal position--forward and back, vertical position, roll, pitch and yaw. These prior art systems do not give adequate positional information, especially when the vehicle is positioned directly in front of the target, to guide the vehicle accurately.